T1IK CRETACEOUS SYSTEM 501 



Tin hiulit-t lay.-!- i- ;i jvile-pink limestone with few fossils. Thus 

 the Red Chalk appears to be a condensed representative of the 

 whole Selbornian stage. 



It appears again near Welton and Willoughby in Lincolnshire, 

 where it is 10 to 12 feet thick, but thins again to 4 or 5 near 

 Caistor. In South Yorkshire the beds are about 7 feet thick, 

 thinning to the north-east, till at Leavening and Wharram it is 

 K than 2 feet, its base containing pebbles of quartz and ironstone. 

 Eastward, however, it expands, and at Speeton it is represented by 

 over 30 feet of material as below : 



Feet. 

 Smooth and firm red marl ....... about 4 



Red marl, enclosing lumps of harder and more calcareous 



material, with many fossils ...... ,,16 



Tough red marly chalk in irregular beds . . . . ., 10 



Red, yellow, and green clays, shaly and gritty . . . ,, l 



The lowest beds contain Bel. minimus and Inoceramus sulcatus, 

 the higher hold Terebratula biplicata, T. capillata, Kingena lima, 

 etc. 



Lower Chalk. This stage as developed in the south of 

 England is divisible into two parts or zones, the lower part forming 

 the zone of Schlcenbachia varians, and the higher part that of 

 Holaster subylobosus. At the base, and included in the range of 

 >''/<, varians, is the sub-zone of Stauronema Carteri, consisting of 

 sandy glauconitic chalk which is often called the " Chloritic marl" 

 At the top is a band of soft grey marl which is the sub-zone of 

 Actinocamax plenus, often called Belemnite marl from the presence 

 of that Belemnoid. 



At Folkestone the beds composing the Lower Chalk are : I5 



Feet 



/one of Hoi. ( 7. Belemnite marl (with Act. plenus) ... 6 



subglobosusA 6. Whitish chalk in massive beds (few fossils) . . 60 



126 feet {5. Grey chalk in massive beds ..... 60 



f 4. Grey marly chalk ....... 20 



Zone of Sch. I 3. Alternating beds of grey marl and hard grey chalk 



varians, ! with many fossils . . . . . .22 



68 feet I 2. Grey chalk with reefs of sponges (Plocoscyphia) . 10 



1 1. Soft green glauconitic chalk (Stauronema) . . 16 



194 



The Lower Chalk attains its greatest thickness in Wiltshire, 

 where it is about 250 feet, the greater part belonging to the zone 

 of Sch. varians, which includes beds of a peculiar siliceous chalk 

 containing imperfect Hints. 



In the Isle of Wight the best exposure of the Lower Chalk is 

 in the Culver Cliffs north of Sandown (see map, Fig. 172), where 



